786 BULLETIN UNITED STATES GEOLOGICAL SUEVEY. 



} Dentary bones arched, well separated except at their symphysis. 



§. Air-bladder suspended in the abdominal cavity, surrounded by many convolu- 

 tions of the long alimentary canal. {Camjyostoma- 

 tinas.) 

 1). Teeth 4-4 or 1, 4-4, 0, -with oblique grinding surface, scarcely hooked; 

 mouth small, inferior ; upper jaw protractile ; 

 dorsal over, or slightly posterior to ventrals ; 

 base of anal short ; alimentary canal 6 to 9 times 

 the length of the body ; no barbel . . Cawpostoma. 

 §§. Air-bladder contiguous to the roof of the abdominal cavity, and above the 



alimentary canal. 

 1[. Intestinal canal elongate, more than twice the length of the body; 

 peritoneum usually more or less black ; premax- 

 illaries projectile. {Choiidrostomatmos.) 

 d. Each jaw provided with a firm, hard, straight, cartilaginous plate, that 

 ofihelowerjaw hard and conspicuous; peritoneum 

 black; intestinal canal elongate. {Chondrostoma- 

 tincB. ) 

 c. Teeth 5-4, club-shaped, entire, hooked, with a broad, oblique grinding 

 surface ; dorsal fin slightly behind ventrals ; 

 anal base scarcely elongate (rays 9) ; caudal fin 

 very long, with numerous accessory rays recur- 

 rent on the caudal peduncle ; scales ratht r small, 

 loosely imbricated ; lateral line present ; upper 



jaw protractile Ackochilus. 



dd. Jaws without conspicuous horny plate. 



e. Teeth 6-6, comiiressed, lanceolate, erect, very slightly bent inward; 

 lower jaw sharp-edged, with a knob at the sym- 

 physis ; dorsal over ventrals ; basal caudal rays 



largely developed; scales small Orthodon. 



ee. Teeth 4-4. 

 /. Teeth cultriform, with oblique grinding surface and little or no 

 hook; lips attenuate, without sheath; rudiment- 

 ary dorsal ray firmly attached to the first devel- 

 oped ray. 

 g. Lateral line complete ; dorsal over ventrals ; mouth horizontal 



— Scales very small Zophendum.* 



Scales large Hybognathus. 



gg. Lateral line incomplete; dorsal behind ventrals; mouth 



oblique Coliscus. 



ff. Teeth short, with grinding surface, and a small hook; rudi- 

 mentary dorsal ray separated from the first de- 

 veloped ray by membrane; dorsal scales small. 



h. Lateral line incomplete ; no barbel Pimephales. 



hh. Lateral line complete; maxillary with a rudimentary or obso- 

 lete barbel Hyborhynchus. 



eee. Teeth 5-5 or 5-4, with grinding surface and hook ; dorsal behind 

 ventrals. 

 i. Lateral line incomplete ; anal base short ; scales verj'^ small. 



Chrosomus. 

 a. Lateral line comijlete; anal base elongate; scales moderate; 



basal caudal rays largely developed Lavinia. 



HIT. Intestinal canal short, little if any longer than the body ; peritoneum 

 mostly white. {Leuciscince.) 

 j. Teeth raptatorial, those of the main row more or less hooked. 



* Zophendum, gen. nov. ; type '^ Hyborhynclms" siderius Cope. 



